A new sub-variant of the novel coronavirus called XBB was dramatically announced earlier this week in Singapore. New COVID cases more than doubled in a day, from 4,700 on Monday to 11,700 on Tuesday – and XBB is almost certainly the reason. The same sub-variant has also just appeared in Hong Kong.
A highly mutated descendant of the Omicron variant of the SAR-CoV-2 virus that caused a record wave of infections starting about a year ago, XBB is in many ways the worst form of the virus to date. It is more contagious than any previous variant or sub-variant. It also evades antibodies from monoclonal therapies, potentially rendering an entire class of drugs ineffective as COVID treatments.
“It’s probably the most immune and poses challenges for current monoclonal antibody-based treatments and prevention strategy,” Amesh Adalja, a public health expert at the Johns Hopkins Center for Health Security, told The Daily Beast. with reference to XBB.
That’s the bad news. The good news is that the new “bivalent” vaccine boosters from Pfizer and Moderna seem to work very well against XBB, even though the original vaccines are less effective against XBB. they won’t prevent everything infections and reinfections, but they should significantly reduce the risk of serious infection that can lead to hospitalization or death. “Even with immuno-evasive variants, vaccine protection against what matters most – severe disease – remains intact,” Adalja said.
As the novel coronavirus evolves to become more contagious and more resistant to certain types of medication, keeping up to date with your reminders is “the most impactful thing you can do in anticipation of what might happen,” expert Peter Hotez in vaccine development at Baylor College, The Daily Beast told The Daily Beast.
Scientists first identified XBB in August. It is one of several major sub-variants that have evolved from the base Omicron variant, accumulating more and more mutations on key parts of the virus, in particular the spike protein, the part of the virus that helps it grab and infect our cells.
XBB has at least seven new mutations along the peak. Mutations which, taken together, make the subvariant harder for our immune system to recognize – and therefore more likely to evade our antibodies and enter our cells to cause infection.
This accumulation of mutations is not surprising. Changes along the spike protein have characterized most major new SARS-CoV-2 variants and subvariants as the pandemic approaches its fourth year.
What is surprising is the competition with XBB as it battles to become the next dominant form of the novel coronavirus. Several other Omicron sub-variants are also in circulation. All are highly evolved. Many of them actually share a subset of key mutations, especially on the peak.
So, while XBB seems to be gaining traction in Asia, a close cousin of XBB called BQ.1.1 is spreading fast in Europe and some US states. There are others also in the running, including BA.2.75.2. Hotez calls these viral cousins the “Scrabble” subvariants, a nod to classic puns and the jumble of scientific designations of closely related viruses.
Scrabble variants are indicative of what scientists call “convergent evolution.” That is, separate viral sublines that pick up more and more of the same mutations. It’s as if the children of Omicron all separately learn how to be a better virus than their parent and become more like each other in the process.
Immune evasion is the common quality. At least two of Scrabble’s subvariants – XBB and BQ.1.1 – are nearly unrecognizable to existing antibody therapies and somewhat less recognizable by the antibodies produced by the first doses of the main messenger RNA vaccines.
By eluding some of our therapies and, to a lesser extent, our original vaccines, XBB and its cousins show us where the new coronavirus is heading, genetically speaking. The current spike in infections in places like Singapore is a preview of a potential global surge this winter or next spring as XBB or one of its kin becomes dominant everywhere.
It is possible to mitigate the worst results. Natural antibodies from a past infection are always the best and longest lasting antibodies. They don’t last forever. But while they do last — a few months or potentially an entire year — the chance of catching a bad case of COVID is pretty low.
So if you had an earlier form of Omicron — say, during the wave of infections that started last Thanksgiving and peaked around February — you might still have good antibodies for a few months. More than enough time to boost those fading natural antibodies with a dose of the latest mRNA boosters.
Pfizer and Moderna formulated these new boosters to include genetic instructions specifically to attack the BA.5 subvariant of Omicron, which is still the dominant form of SARS-CoV-2 but is rapidly disappearing as XBB and the other subvariants Scrabble variants surpass it.
Bivalent boosters should work fairly well against virus forms closely related to BA.5, including Scrabbles. “This is because one of the two components [in the boosters] induces an immune response to BA.5, and most new Scrabble variants are more like BA.5 than [the] original Chinese line,” Hotez told The Daily Beast.
The implication, of course, is that we will eventually need another new booster to keep pace with the rapidly changing virus. Of course, bivalent boosters work against immediate descendants of BA.5 and BA.5. But what about the next generation of Omicron sub-variants, the one after XBB and its cousins?
More and more health officials are turning to the idea of an annual COVID booster. US President Joe Biden even endorsed the idea in a statement last month. “As the virus continues to change, we will now be able to update our vaccines every year to target the dominant variant,” Biden said. “Like your annual flu shot, you should get it between Labor Day and Halloween.”
But one booster a year might not be enough if, as some epidemiologists fear, natural antibodies fade more quickly and the novel coronavirus mutates at an accelerated rate. One concern, if it turns out that we need new boosters twice a year, is whether industry can develop new vaccines fast enough and whether health agencies can approve them quickly.
There’s an even bigger question, though. “The biggest factor is just that people get a more recent booster,” James Lawler, an infectious disease expert at the University of Nebraska Medical Center, told The Daily Beast.
Even if a new booster is available every six months or so, will enough people get it to make a difference to the overall rates of serious illness and death? Booster use is down globally, but especially so in the United States, where only 10% of people have received the bivalent booster since federal regulators approved them in August.
XBB is a nasty little sub-variant. But that’s not the last word on COVID. The novel coronavirus will continue to mutate and find new ways to evade our antibodies whether many people pay attention or not.
The virus is not done with us. Which means we can’t end this. Be boosted. And prepare to be boosted Again in 2023.